Interactions of Eu(III) and ²⁴³Am(III) with humic acid-bound γ-Al₂O₃ studied using batch and kinetic dissociation techniques

The association of Eu(III) and ²⁴³Am(III) with humic acid-bound γ-Al₂O₃ (HA-Al₂O₃) was investigated using batch technique and the kinetic dissociation properties were studied using chelating resin. The results indicated that Eu(III) and ²⁴³Am(III) had very similar sorption properties. The kinetics of desorption of ²⁴³Am(III) from HA-Al₂O₃ hybrids were studied at three different pH values (pH 4.0, 5.0 and 6.0) after aging time for 2h, 4days, and 1month by adding chelating resin to remove the desorbed free ²⁴³Am(III) ions from the HA-Al₂O₃ hybrids. The fraction of ²⁴³Am(III) on the irreversible binding sites of the HA-Al₂O₃ hybrids increased as the pH increased. Two different ²⁴³Am(III)-HA-Al₂O₃ species (i.e., "fast" and "slow" dissociation kinetics, which represented the "weak" and "strong" species on reversible sites) were required to fit the kinetic dissociation results. Although ²⁴³Am(III) was initially a "fast" dissociating species, it became a "slow" dissociating species as the aging time increased and at low HA concentrations. When the HA concentration was high, the "fast" and "slow" dissociating species of ²⁴³Am(III) bound to HA-Al₂O₃ particles were not influenced by the aging time. These results describe the physicochemical behavior of trivalent lanthanides and actinides in the natural environment, which is important to understand the potential pollution of long-lived radionuclides.